The present invention relates to an ink-jet printing head for electrically conductive ink, comprising an electrically insulating container for the ink, closed by a flexible diaphragm, the container having a nozzle for the selective emission of droplets of ink, an electrode in contact with the ink and a counter-electrode which is adjacent to the nozzle, emission of droplets of ink being caused by an electrical voltage pulse between the counter-electrode and the electrode.
In known printers of the above-indicated type, vapours or bubbles are formed in the ink during the during the printing operation. These accumulate in the container and have to be removed from the nozzle in order to prevent the emission of droplets therefrom from being blocked.
In order to remedy this disadvantage, a printing head has already been proposed wherein the container is closed by a flexible diaphragm which is spring-loaded so as to create a certain depression in the container and thus to cause bubbles to collect in the space formed between the ink and the diaphragm, as the ink is consumed. Because of the above-mentioned spring however, the head is complicated and requires a certain space to permit expansion of the cartridge.
A printing head has also been proposed wherein the container is provided with a hole to permit atmospheric pressure to be maintained on the ink. That head suffers from the disadvantage that ink is lost from the head in the event of the head being inverted or if it is transported, for example by air.